1. Field of the Invention
This application is directed to a subsurface safety valve system for use in drilling oil or gas wells. Such valves are commonly used to prevent flow of oil or gas from the well to the surface when certain conditions occur.
2. Description of Related Art
Currently such safety valves are held in an open position by virtue of pressure in a control line from the surface acting on a piston in the valve which is operatively connected to a flow sleeve which moves axially to open a valve member. Movement of the sleeve also compresses a spring surrounding the flow sleeve.
Upon the occurrence of an unfavorable event, the pressure is relieved via the control line so that the spring will move the flow sleeve upwardly so as to allow the valve, which may be a flapper valve as shown in FIG. 2 of this application to close. In so doing, the spring must overcome the pressure head caused by the hydraulic fluid and the flow resistance due to the small diameter of the control line.
Some control lines in deep water subsea wells may be up to two miles or more in length and may extend a vertical distance of more than a mile.
Consequently the pressure head and resistance to flow is quite high which can delay the response time for the valve and may in some cases result in failure.